Jessica fears Losing Justin Timberlake to Britney Spears!

"Jessica burst into tears when she heard Justin had secretly called Britney while she was in rehab and says he still thinks she is a great woman," said a source.

Last week PEOPLE reported that Justin Timberlake was so concerned about Britney Spears, who entered rehab in February, that he reached out to her.

"I called her because I worried about her," Timberlake, 26, said recently at a press day for his new movie Shrek The Third.

"She's a great woman. I'm rooting for her," he said. "[It] seems like she's getting everything under control now."

"Jessica is crazy about Justin. Scarlett Johannson was her first obstacle, now she sees Britney as a threat. Britney is the only girl who broke Justin's heart- and Jessica knows it."

Since they began dating the two have spent lots of time together and things have been great. But then Justin revealed that he called Britney at the Promises rehab center in Malibu. And now Jessica fears that Britney could wreck their romance. the source revealed:

"Jessica knows how Britney loves to flirt, and she's terrified, now that Justin has admitted he still cares for her, that Britney will try to get him back."